Heat controlled optoelectrical unit

ABSTRACT

The present invention relates to heat control and cooling of an optoelectrical unit, which converts between electrical and optical signal formats. The optoelectrical unit contains at least one optoelectrical capsule positioned on a circuit board. A primary heat sink is adapted to receive heat energy dissipated from the capsule. The capsule is oriented on the circuit board, such that it presents a relatively small footprint thereon and, at the same time, rises relatively large area sides, which do not face directly towards the circuit board. The primary heat sink has at least one cavity, which is adapted to the shape and dimensions of the capsule, such that the cavity contains at least one capsule. The primary heat couples thermally well to the capsule. Furthermore, the capsules assist in aligning the primary heat sink in its intended position.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

[0001] The present invention relates generally to heat control andcooling of optical communication equipment. More particularly theinvention relates to an optoelectrical unit for converting informationsignals between an electrical signal format and an optical signal formataccording to the preamble of claim 1.

[0002] Optical communication systems transport information in the formof modulated light signals. A laser module, e.g. a semiconductor laser(laser=light amplification by stimulated emission of radiation) in asignal transmitter unit is here normally used in order to accomplish theoptical signals based on electrical ditto, and a photodetection module,e.g. a photodiode, in a signal receiver unit typically converts theoptical signals back into electrical signals again. In most cases, thesignal transmitter and a corresponding signal receiver are co-located toform an optoelectrical transceiver unit. These units, in turn, normallyoperate in an environment that includes one or more other units thatdissipate comparatively large amounts of heat energy, such that theambient temperature becomes fairly high. It is therefore particularlyimportant that the transceiver unit itself is efficiently cooled.

[0003] The above transmitter and receiver units should generally be assmall as possible with the aim of concentrating the number of processedinformation bits per physical volume unit and thereby reduce the overallsize of the optical communication equipment.

[0004] For the same reason, the transmitters and receivers should alsobe placed as close as possible to each other. However, thephotodetection module and the laser module in particular produce arelatively large amount of power losses in the form of heat energy,which must be transported away from the equipment in order to maintainan acceptable working temperature. Normally, there are also restrictionsas to the amount of heat energy that may be discharged from a particularunit in order to guarantee that the temperature of any neighboring unitsstays within an acceptable range. Additionally, there may be a safetyincentive to limit the equipment's temperature so as to reduce the riskof burn injuries on the personnel that operate or service the equipment.

[0005] In the prior-art transceivers, the transmitter and receiver unitsare most commonly placed in a respective indentation in the circuitboard. Furthermore, the units are usually oriented with their largestside in parallel with the circuit board, such that they show a largestpossible interface area towards a heat sink below and/or above thecircuit board.

[0006] Classically, the heat power losses increase with increasedprocessing speeds/bitrates. A large amount of heat energy, in turn,requires a relatively large interface area towards a cooling medium inorder to not result in excessive equipment temperatures. Hence,increasing the ratio of processing capacity per volume or area unitimplies a non-trivial optimization problem.

SUMMARY OF THE INVENTION

[0007] The object of the present invention is therefore to provide anoptoelectrical unit, which alleviates the problem above and thus offersa solution that is comparatively efficient with respect to theprocessing capacity per volume unit, and at the same time, enables anadequate dissipation of the heat power losses.

[0008] According to the invention the object is achieved by theinitially described optoelectrical unit for converting informationsignals between an electrical and an optical signal format, which ischaracterized in that the unit comprises at least two capsules whicheach of contains a particular warmest side that radiates more heatenergy than any one of the other sides of the respective capsule.Moreover, two of the at least two the two capsules are positioned inrelative proximity to each other on the circuit board with their warmestsides substantially perpendicular to each other, such that the twocapsules form a general L-shape pattern on the circuit board.

[0009] This design is most advantageous, since it combines an efficientusage of the circuit board area with a competent cooling of theoptoelectrical capsules.

[0010] According to a preferred embodiment of the invention, the warmestside of the capsule is one of the relatively large area sides. Thisdesign namely improves the possibilities of accomplishing an efficientcooling via, for example, an air cooled heat sink along the warmestside.

[0011] According to another preferred embodiment of the invention, theat least one capsule has the general shape of a rectangularparallelepiped with two relatively large area sides and four relativelysmall area sides. Naturally, this does not imply that the capsule shapemust represent a mathematically perfect rectangular parallelepiped. Onthe contrary, its sides may be more or less tilted with respect to eachother, such that they are either all pair wise parallel to each other orat least two opposite sides being non-parallel to each other. Forexample, the capsule may describe a truncated pyramid. Moreover, one ormore of the capsule's edges and/or corners may be rounded. In any case,the capsule is positioned on the circuit board such that its relativelylarge area sides are oriented substantially perpendicular to a componentside of the circuit board. An advantage accomplished by placing thecapsule on its edge like this is that the capsule thereby not only showsa relatively small footprint on the circuit board, a relatively largecapsule area also becomes readily accessible for cooling by means of theprimary heat sink.

[0012] As mentioned initially, one capsule may contain a laser unit,which receives a first electrical information signal and produces inresponse thereto a first optical information signal. Correspondingly,another capsule may contain a photodetection unit, which receives asecond optical information signal and produces in response thereto asecond electrical information signal.

[0013] According to a preferred embodiment of the invention, the primaryheat sink has at least one coupling surface, which is adapted to theshape and dimensions of the optoelectrical capsule. Specifically, thismeans that the coupling surface is substantially parallel and relativelyproximate to at least one side of the capsule. A good thermal couplingis thus accomplished between the capsule and the primary heat sink.

[0014] According to another preferred embodiment of the invention, theoptoelectrical unit includes at least one thermo conductive gap fillerbetween at least one optoelectrical capsule and at least one couplingsurface. The thermo conductive gap fillers are primarily intended toenhance the thermal coupling between the capsule and the primary heatsink by filling any air gap there between. The thermo conductive gapfillers are, however, also advantageous because they assist inaccomplishing a good mechanical fit between the capsule and the primaryheat sink.

[0015] According to yet another preferred embodiment of the invention,the primary heat sink includes at least one cavity, which is adapted tothe shape and dimensions of at least one of the capsules. The cavitycontains at least two cavity sides that are substantially parallel andrelatively proximate to at least two sides of the capsule. This isadvantageous, since the thermal coupling between the capsule and theprimary heat sink is thereby enhanced.

[0016] According to a further preferred embodiment of the invention, thetwo cavity sides above are substantially parallel and relativelyproximate to two sides of each of the at least one capsule, which arealso mutually parallel to each other. In other words, the primary heatsink at least partly surrounds the capsule. Naturally, this ispreferable, since a comparatively large amount of heat energy from thiscapsule can thereby efficiently be absorbed by the heat sink. Moreover,the heat sink assists efficiently in holding the capsule in a fixedposition on the circuit board.

[0017] According to another preferred embodiment of the invention, theprimary heat sink is also adapted to receive heat energy, which isdissipated from at least one circuit element .on the circuit board inaddition to the least one capsule. Such combined heat sink function isadvantageous, since it not only facilitates the assembly of theoptoelectrical unit. Additionally, the total heat sink capacity isthereby utilized very efficiently. Furthermore, during operation of theunit, the temperature distribution becomes more uniform across the unit.This is in turn desirable, since any mechanical stress on the unitresulting from thermal expansion is thus reduced.

[0018] According to a further preferred embodiment of the invention, theprimary heat sink contains at least two surfaces, which aresubstantially parallel and relatively proximate to at least the warmestsides. This warrants for a good thermal coupling between the capsule andthe heat sink.

[0019] According to yet another preferred embodiment of the invention,the optoelectrical unit comprises a secondary heat sink in addition tothe primary heat sink. The secondary heat sink is positioned such thatit adjoins the primary heat sink. Heat energy may thereby be transportedbetween the primary heat sink and the secondary heat sink by means ofthermo conduction. This is advantageous, since the total heat sinkcapacity is thereby utilized very efficiently. Moreover it vouches for acomparatively uniform temperature distribution over the unit, which inturn is desirable, for instance from a mechanical stress point of view.

[0020] According to a further preferred embodiment of the invention, thesecondary heat sink contains an opening, which is adapted to the shapeand dimensions of the primary heat sink such that the secondary heatsink adjoins at least two sides of the primary heat sink. Hence, heatenergy may efficiently be transported between the two heat sinks.Preferably, the secondary heat sink completely surrounds the primaryheat sink, such that the primary heat sink and the secondary heat sinkform a joint outer surface of the optoelectrical unit.

[0021] According to a still further preferred embodiment of theinvention, the secondary heat sink is also adapted to receive heatenergy from at least one circuit element outside the coverage area ofthe primary heat sink. Thus, the heat sink arrangement's coolingcapabilities become effective for other units than the optoelectricalcapsules, which generally is desirable. Preferably, a thermo conductivegap filler is included between said at least one circuit element and thesecondary heat sink. This namely both enhances the thermo conductivecoupling there between and accomplishes a good mechanical fit betweenthe capsule and the heat sink.

[0022] To sum up, the invention offers a highly efficient solution forcooling communication equipment in the form of optoelectrical units.Thereby the temperature of these units, as well as any neighboringunits, may be maintained within a well-defined range. Naturally, theinvention will therefore provide a competitive edge to any communicationsystem where optical transmitters are utilized for the transmission ofinformation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention is now to be explained more closely bymeans of preferred embodiments, which are disclosed as examples, andwith reference to the attached drawings.

[0024]FIG. 1 shows a capsule containing a laser unit according to anembodiment of the present invention,

[0025]FIG. 2 shows a capsule containing a photodetection unit accordingto an embodiment of the present invention,

[0026]FIG. 3 shows an exploded diagram over a laser capsule according toan embodiment of the invention,

[0027]FIG. 4 depicts a circuit board according to an embodiment of theinvention, which comprises the capsules shown in FIGS. 1-3,

[0028]FIG. 5a shows a bottom-view of a primary heat sink according to anembodiment of the invention,

[0029]FIG. 5b shows a corresponding top-view of the primary heat sinkaccording to the embodiment shown in FIG. 5a, and

[0030]FIG. 6 represents an exploded diagram over an entireoptoelectrical unit according to an embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0031] Conventionally, the optoelectrical units (such as lasers andphotodetectors) in optoelectrical transceivers have been oriented withtheir largest side in parallel with the circuit board on which they aremounted. A largest possible interface area has thereby been accomplishedtowards at least one heat sink being placed either below, above or bothbelow and above the circuit board. This design, however, results in arelatively large footprint for each optoelectrical unit, which in turnconsumes valuable circuit board area that could have been used by otherunits. Therefore, the present invention proposes that the optoelectricalunits instead be placed on their edges, i.e. with a capsule side havinga comparatively small area towards the circuit board. FIG. 1 shows afirst example of this strategy, where a capsule 100 containing a laserunit stands on one of its relatively small area sides 101 d. The lasercapsule 100 is presumed to have the general shape of a rectangularparallelepiped with two relatively large area sides 101 a; 101 b andfour relatively small area sides 101 c, 101 d, 101 e and 101 f. Thelatter may either all have substantially the same size, or asillustrated in FIG. 1, have two somewhat larger sides 101 c; 101 d andtwo somewhat smaller sides 101 e; 101 f. Although the exact relationshipbetween the relatively large area sides 101 a; 101 b and the relativelysmall area sides 101 c-f is not critical for the proposed solution, therelatively large area sides 101 a; 101 b should preferably have at least50% larger area than the largest of the relatively small area sides 101c-f. It is furthermore advantageous, from an assembly point of view, ifthe capsule 100 is mounted such that the relatively large area sides 101a; 101 b are oriented substantially perpendicular to the circuit board.A feedthrough 102 in the bottom side 101 d of the capsule 100 containsone or more electrical leads 103 via which an incoming electrical signalE_(i) is received to the laser unit. Preferably, the electrical leads103 constitute ceramic conductors in the feedthrough 102 in order tomake possible a high lead density. The laser unit produces an outgoingoptical signal λ_(o) in response to the electrical signal E_(i) thatrepresents the. same information. The optical signal λ_(o) is fed outfrom the capsule 100 to an optical fiber (not shown) via an opticalconnector 105, for example of LC-type (Lucent), SC-type (subscriberconnector) or MU-type (NTT). Here, the optical connector 105 is attachedto one of the relatively small area sides 101 e. Technically however, itmay equally well be attached to one of the relatively large area sides101 a or 101 b.

[0032] According to a preferred embodiment of the invention, one of therelatively large area sides 101 a radiates more heat energy than any oneof the other sides 101 b-101 f. I.e. this relatively large area side 101a is the warmest side of the capsule 100. For example, this may be dueto the fact that the laser unit is mounted on the inside of thisparticular side 101 a (see FIG. 3). Preferably, the capsule 100 alsocontains a thermoelectric module (such as a Peltier device), whichactively transports heat energy from the laser unit towards the side 101a of the capsule 100 exterior.

[0033]FIG. 2 shows a second example of a capsule 200 that contains anoptoelectrical unit according to an embodiment of the present invention.In analogy with the capsule 100 shown in FIG. 1 above, thephotodetection capsule 200 is presumed to have the general shape of arectangular parallelepiped with two relatively large area sides 201 a;201 b and four relatively small area sides 201 c, 201 d, 201 e and 201f. The photodetection capsule 200 is intended to stand on one of itsrelatively small area sides 201 d on a circuit board. As is apparentfrom the figure, the relatively small area sides 201 c-f all haveapproximately the same size. However, the relatively small area sides201 c-f may equally well have sizes, which are substantially differentin pairs, i.e. represent two somewhat larger sides and two somewhatsmaller sides. Although again, the exact relationship between therelatively large area sides 201 a; 201 b and the relatively small areasides 201 c-f is not critical for the proposed solution, the relativelylarge area sides 201 a; 201 b should preferably have at least 50% largerarea than the largest of the relatively small area sides 201 c-f. It isfurthermore advantageous, from an assembly point of view, if the capsule200 is mounted such that the relatively large area sides 201 a; 201 bare oriented substantially perpendicular to the circuit board.

[0034] According to a preferred embodiment of the invention, the capsule200 receives an incoming optical signal λ_(i) from, for example, anoptical fiber (not shown) via an optical connector 205 on one of thecapsule's 200 relatively large area sides 201 b. Preferably, if theoptical connector 105 referred to above is attached to one of therelatively small area sides 101 c-f of the laser capsule 100, theoptical connector 205 should be attached to one of the relatively largearea sides 201 a or 201 b of the photodetection capsule 200, and viceversa. The optical connector 205 may for instance be of LC-type(Lucent), SC-type (subscriber connector) or MU-type (NTT). Thephotodetection unit within the capsule 200 converts the optical signalλ_(i) into a corresponding electrical signal E_(o) that represents thesame information. A feedthrough 202 in a bottom side 201 d of thecapsule 200 contains one or more electrical leads 203 via which theelectrical signal E_(o) is delivered to other circuit elements forfurther processing. Preferably, the electrical leads 203 constituteceramic conductors in the feedthrough 202 in order to make possible ahigh lead density.

[0035] According to a preferred embodiment of the invention, one of therelatively large area sides 201 a radiates more heat energy than any oneof the other sides 201 b-201 f and is thus the warmest side of thecapsule 200. For example, this may be due to the fact that thephotodetection unit is mounted on the inside of this particular side 201a. The capsule 200 may also contain a thermoelectric module (such as aPeltier device), which actively transports heat energy from thephotodetection unit towards the warmest side 201 a of the capsule 200exterior.

[0036]FIG. 3 shows an exploded diagram over a laser capsule 100according to an embodiment of the invention. Here, an optoelectricalcomponent in the form of a laser unit 310 is mounted on the inside of aside 101 a of the laser capsule 100. A control circuitry 320 for thelaser unit 310 is in turn positioned on top of this unit 310.Preferably, the capsule 100 also contains a thermoelectric module (notshown), which actively transports heat energy from the laser unit 310towards the exterior of the capsule side 101 a. A capsule side 101 b inthe form of a lid is used to seal the capsule 100 after assembly of theunits therein.

[0037]FIG. 4 depicts a circuit board 400 according to an embodiment ofthe invention, which comprises a laser capsule 100 and a photodetectioncapsule 200 as described above. Both these capsules 100 and 200 arepositioned on the circuit board 400 such that their relatively largearea sides 101 a, 101 b and 201 a, 201 b respectively are orientedsubstantially perpendicular to a component side of the circuit board400. For a given width D of the circuit board 400, this leaves arelatively large front space d_(f) that can be used for other purposesthan connecting optical fibers, for example displays (not shown) toindicate a transceiver status. Moreover, the distance d_(Δ) between theoptical connectors 105 and 205 can thereby be made comparatively short.

[0038] The capsules 100 and 200 are here presumed to have a respectivewarmest side 101 a and 201 a. Preferably, the capsules 100 and 200 arepositioned relatively close to each other with their warmest sides 101a; 201 a substantially perpendicular to each other, such that thecapsules 100 and 200 form a general L-shape pattern on the circuit board400. The circuit board 400 may also include a first circuit 430 and asecond circuit 440 in addition to the capsules 100 and 200, for instancefor pre- and post-processing of the electrical signals E_(i) and E_(o).

[0039]FIG. 5a shows a bottom-view of a primary heat sink 500 accordingto an embodiment of the invention, which is to be placed on top of thecapsules 100 and 200 when mounted on a circuit board 400, as describedwith reference to FIG. 3 above. The primary heat sink 500 contains afirst cavity 510, which is adapted to the shape and dimensions of thelaser capsule 100 and a second cavity 520, which is adapted to the shapeand dimensions of the photodetection capsule 200. The cavities 510 and520 each contains a multitude of so-called coupling surfaces 510 a, 510b, 510 c and 510 f respective 520 a, 520 b, 520 c and 520 f. Thecoupling surfaces 510 a, 510 b, 510 c, 510 f, 520 a, 520 b, 520 c and520 f are cavity sides that are substantially parallel and relativelyproximate to the same number of sides of the respective capsule 100 and200 when the primary heat sink 400 is placed in its intended position. Agood thermal coupling is thereby accomplished between the capsules 100;200 and the primary heat sink 500.

[0040] According to a preferred embodiment of the invention, the primaryheat sink 500 is designed such that it contains at least two surfaces,which are substantially parallel and relatively proximate to at leastsaid warmest sides 101 a and 201 a of the capsules 100 and 200. In FIG.5a, the cavity side 510 a of the first cavity 510 respective the cavityside 520 a of the second cavity 520 represent these surfaces.

[0041] Preferably, the cavities 510 and 520 contain two cavity sides(coupling surfaces) 510 a and 510 b respective 520 a and 520 b, whichare mutually parallel to each other and that are substantially paralleland relatively proximate to at least two sides 101 a, 101 b; 201 a, 201b of the respective capsule 100 and 200 when the primary heat sink 500is placed in its intended position over the capsules 100 and 200. Thisensures a first-class thermal coupling between the capsules 100; 200 andthe primary heat sink 500. Furthermore, it accomplishes a goodmechanical fit between the capsules 100 and 200 and the primary heatsink 500, such that the capsules 100 and 200 assist in lining up theprimary heat sink 500 in its intended position. An efficient cooling ofthe capsules 100 and 200 is thus achieved, even in case one of thecapsules 100 and 200 (for some reason) is slightly misaligned from itsintended position.

[0042] According to another preferred embodiment of the invention, theprimary heat sink 500 is also designed such that it covers at least apart of at least one of the first circuit element 430 and the secondcircuit element 440 (see FIG. 6). The primary heat sink 500 is hencecapable of receiving heat energy being dissipated from this(these)circuit element(s).

[0043] A semi-transparent top-view of the primary heat sink 500 shown inFIG. 5a is illustrated in FIG. 5b. The heat sink 500 preferably hasplanar inner surfaces and may, but need not, be equipped with radiatingfins on its topmost outer surface.

[0044]FIG. 6 represents an exploded diagram over an entireoptoelectrical unit according to an embodiment of the invention. Thecircuit board 400 comprises a laser capsule 100, a photodetectioncapsule 200 and three other circuit elements 430, 440 and 450respectively. The capsules 100 and 200 and the first and second circuitelements 430; 440 are positioned in accordance with what has beendescribed with reference to the FIGS. 4 and 5a above.

[0045] A first thermo conductive gap filler, e.g. a thermo conductivepad, silicone or an equivalent gel 612 is attached on the top faceand/or at least one side face of the capsules 100 and 200 in order toenhance the thermal coupling between the relevant capsule(s) 100; 200and the primary heat sink 500. A corresponding second gap filler 610 isattached to the warmest side of the laser capsule 100. Likewise, a thirdgap filler 634 is attached on the upper surfaces of the first circuitelement 430 and the second circuit element 440.

[0046] The primary heat sink 500 is fitted onto the capsules 100 and 200after attaching the gap fillers 610, 612 and 634. Moreover, the firstand second gap fillers 612 and 610 thereby removes any play between thecapsules 100; 200 the primary heat sink 500. The capsules 100 and 200thus assist in lining up the primary heat sink 500 in its intendedposition.

[0047] According to the illustrated embodiment of the invention, theoptoelectrical unit comprises a secondary heat sink 600, whichphysically adjoins the primary heat sink 500, such that heat energy maybe transported between the primary heat sink 500 and the secondary heatsink 600 by means of thermo conduction. Preferably, the secondary heatsink 600 contains an opening, which is adapted to the shape anddimensions of the primary heat sink 500 so as to adjoin at least twosides of the primary heat sink 500. For example, the secondary heat sink600 may completely surround the primary heat sink 500 (as shown in FIG.6) and hence accomplish an excellent thermal coupling between the units500 and 600. Furthermore, the heat sinks 500; 600 may be designed suchthat they form a joint outer surface of the optoelectrical unit. Roughlyspeaking, this means that the optoelectrical unit constitutes a sealedtight unit, which in turn, implies advantageous environmental attributesand provides a good electromagnetic compatibility (EMC) respectiveshielding against electromagnetic Interference (EMI).

[0048] According to a preferred embodiment of the invention, thesecondary heat sink 600 is adapted to receive heat energy from a thirdcircuit element 450 on the circuit board 400, which is positionedoutside a coverage area of the primary heat sink 500. A fourth thermoconductive gap filler 635 is preferably attached on the upper surface ofthis circuit element 450 in order to ensure a good thermal coupling alsobetween the circuit element 450 and the secondary heat sink 600.Naturally, the third circuit element 450 may equally well be located ona different circuit board than the circuit board 400, which containse.g. the capsules 100; 200 and any circuit elements 430; 440.

[0049] The term “comprises/comprising” when used in this specificationis taken to specify the presence of stated features, integers, steps orcomponents. However, the term does not preclude the presence or additionof one or more additional features, integers, steps or components orgroups thereof.

[0050] The invention is not restricted to the described embodiments inthe figures, but may be varied freely within the scope of the claims.

1. An optoelectrical unit for converting information signals between anelectrical signal format and an optical signal format comprising: acircuit board which contains at least two optoelectrical capsules, theat least two capsules being positioned on the circuit board such thattheir respective footprint towards the circuit board has a smaller areathan the area of a largest side of the capsule, and a primary heat sinkadapted to receive heat energy being dissipated from at least one of theat least two optoelectrical capsules wherein each of the at least twocapsules contains a particular warmest side radiating more heat energythan any one of the other sides of the respective capsule, and two ofthe at least two capsules are positioned in relative proximity to eachother on the circuit board with their warmest sides substantiallyperpendicular to each other such that the two capsules form a generalL-shape pattern on the circuit board.
 2. An optoelectrical unitaccording to claim 1, wherein the warmest side is one of the relativelylarge area sides.
 3. An optoelectrical unit according to claim 1,wherein each of the at least two capsules has the general shape of arectangular parallelepiped with two relatively large area sides and fourrelatively small area sides, and the at least two capsules arepositioned on the circuit board such that their relatively large areasides are oriented substantially perpendicular to a component side ofthe circuit board.
 4. An optoelectrical unit according to claim 3,wherein the primary heat sink comprises at least one coupling surfaceadapted to the shape and dimensions of at least one of the at least twooptoelectrical capsules such the at least one coupling surface issubstantially parallel with and relatively proximate to at least oneside of said at least two capsules.
 5. An optoelectrical unit accordingto claim 4, wherein the unit comprises at least one thermo conductivegap filler between at least one of the at least two optoelectricalcapsules and at least one of the at least one coupling surface.
 6. Anoptoelectrical unit according to claim 4, wherein the primary heat sinkcomprises at least one cavity adapted to the shape and dimensions of atleast one of the at least two capsules such that the at least one cavitycontains at least two cavity sides being substantially parallel with andrelatively proximate to at least two sides of at least one of the atleast two capsules.
 7. An optoelectrical unit according to claim 6,wherein the at least two cavity sides are substantially parallel withand relatively proximate to at least two mutually parallel sides of atleast one of the least two capsules.
 8. An optoelectrical unit accordingto claim 1, wherein the primary heat sink is adapted to receive heatenergy being dissipated from at least one circuit element on the circuitboard in addition to the least two capsules.
 9. An optoelectrical unitaccording to claim 1, wherein the primary heat sink contains at leasttwo surfaces being substantially parallel and relatively proximate to atleast said warmest sides.
 10. An optoelectrical unit according to claim1, wherein the unit comprises a secondary heat sink adjoining theprimary heat sink such that heat energy may be transported between theprimary heat sink and the secondary heat sink by means of thermoconduction.
 11. An optoelectrical unit according to claim 10, whereinthe secondary heat sink contains an opening adapted to the shape anddimensions of the primary heat sink such that the secondary heat sinkadjoins at least two sides of the primary heat sink.
 12. Anoptoelectrical unit according to claim 11, wherein the secondary heatsink surrounds the primary heat sink and that said heat sinks form ajoint outer surface of the optoelectrical unit.
 13. An optoelectricalunit according to claim 10, wherein the secondary heat sink is adaptedto receive heat energy being dissipated from at least one circuitelement outside a coverage area of the primary heat sink.
 14. Anoptoelectrical unit according to claim 1, wherein at least one of the atleast two capsules contains a laser unit receiving a first electricalinformation signal and producing in response thereto a first opticalinformation signal.
 15. An optoelectrical unit according to claim 1,wherein at least one of the at least two capsules contains aphotodetection unit receiving a second optical information signal andproducing in response thereto a second electrical information signal.16. An optoelectrical unit according to claim 1, wherein at least one ofthe at least two capsules contains a thermoelectric module activelytransporting heat energy from an optoelectrical component inside thecapsule towards the exterior of the capsule.
 17. An optoelectrical unitaccording to claim 16, wherein the thermoelectric module includes aPeltier device.